The harbour or common seal (Phoca vitulina) occurs in the North Atlantic and North Pacific. There are about 83,000 harbour seals in Europe. About 35% of this population is found in UK waters, and 83% of these in Scottish waters.

The grey seal (Halichoerus grypus) is found only in the North Atlantic Ocean, the Baltic Sea and the Barents Sea. As one of the rarer seal species, its world population runs to just 350,000 to 400,000 individuals. About 40% of all grey seals live in UK waters – and about 90% of this number live off Scotland.

Harbour seals

Adult harbour seal males weigh about 85kg and measure about 1.45m long. Females aren’t much smaller, at about 75kg and 1.35m. It’s very hard to tell males and females apart. A harbour seal’s face resembles that of a dog.

Harbour seals prefer more sheltered waters and have a more restricted range than grey seals. They tend to travel 40 to 50km from their haul-out site to forage for food.

Strongholds for harbour seals:

Shetland

Orkney

east coast of the Outer Hebrides

most of the Inner Hebrides

west coast of Scotland (from Skye to Arran)

Moray Firth

Firth of Tay

Female harbour seals haul out to give birth at natal breeding sites – i.e. where they themselves were born – within their more restricted range in early summer. Pups are born having already shed their white coat in the womb.

Grey seals

Grey seals are much bigger than harbour seals. Adult males weigh up to 300kg and can be 2m in length, while adult females weigh up to 180kg and are about 1.8m long. Grey seals have a long, sloping 'Roman nose'.

Grey seals travel large distances to forage and favour more exposed coasts and islands. Outside of the breeding season they can be found hauled out on islands and coasts closest to the open sea.

Such areas include the:

outer fringes of Shetland and Orkney

the west coast of the Outer Hebrides

outer islands in the Inner Hebrides

outer sandbanks in the Firth of Tay and the Moray Firth

Large groups of pregnant grey seal females return to traditional breeding sites on rocky coasts in the autumn to give birth. Pups are born with white hair that is moulted over the first three weeks of life.

Grey seal pup startled by a wave

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Grey seal pup startled by a wave

Threats to seals

Threats caused by humans include:

climate change – the most noticeable effects are likely to be changes in the distribution of seals and the availability of prey

disease – such as phocine distemper virus, which devastated harbour seal populations on England’s east coast in 1988 and 2002

orca (killer whales) – orcas have been seen more regularly in Shetland and Orkney, sometimes feeding on harbour or grey seals

Harbour seals in the Northern Isles and on the east coast of Scotland have seen a serious decline since the mid-1990s, but the reason why isn’t yet clear. Several factors may be to blame, including predation, pollution and the effect of climate change on the harbour seal’s prey. In 2012, the Sea Mammal Research Unit began a major programme of research to investigate the decline.